Metabolic dependencies and alterations of papillary thyroid carcinoma cell lines

Thyroid cancer is the most common endocrine malignancy and among the major types, papillary thyroid carcinoma (PTC) represents 90% of all thyroid carcinomas. Several studies have identified in PTC recurrent somatic genetic alterations in known oncogenes (i.e., BRAF, RAS and RET). Recently, hTERT promoter mutations have been observed in approximately 11% of PTC with aggressive behavior, and together with other genetic mutations, like TP53 mutations, have been associated with aggressive forms of PTC. Cancer cells show profound metabolic alterations and a perturbed redox homeostasis, allowing them to meet the metabolic and biosynthetic needs. Redox state, which, together with altered metabolism, is considered a hallmark of cancer cells, is closely dependent on various metabolic pathways, resulting in a crosstalk between metabolism and redox homeostasis. Currently, cancer research and the evaluation of targetable features, have met a new challenge, due to the heterogeinity of tumor and the different cell populations behaviour whitin the tumor mass. Indeed, PTCs, as most tumors, are constituted by a subset of cells, cancer stem cells (CSCs), which are crucially involved in tumor progression and recurrence more than the differentiated tumor cells. CSCs exhibit a distinct metabolic phenotype, supporting tumor growth and survival, but how they adapt their metabolism to the cancer process is still unclear, and no data are yet available for PTC. Understanding this metabolic remodeling and dependence is essential to elucidate the fundamental mechanisms of tumorigenesis as well as to find new therapeutic strategies, targeting cancer metabolism. Among all the possible anti-tumoral compounds, high-dose of vitamin C has been showed to exhibit cytotoxic effect in cancer cells, primarily mediated by pro-oxidant and metabolic effects. However, the exact role of vitamin C in the metabolic perturbation and its potential use as a therapy target in cancer treatment and prevention in PTC in still poorly understood and require further studies. This study aimed to investigate the metabolic alterations and redox status of PTC-derived cell lines in association with the different genetic backgrounds, underlying the metabolic dependencies of PTC differentiated and CSCs cells. Furthermore, vitamin C has been used as anti-tumoral compound, in order to clarify the anti-cancer mechanism and to better understand the metabolic sensitivity of PTC-derived cells. A targeted and untargeted metabolomic approach has been used to investigate the metabolic profile of PTC-derived cells, while molecular analysis, such as immunoglotting, immunofluorescense, fluorimetric assays have been used to better understand the mechanism beyond the metabolic alterations. This approach has led to the understanding of the metabolic features and their association with redox balance and genotypes in PTC-derived differentiated and stem cells. Furthermore, beside the known oxidative effect of vitamin C, our analyses have elucidated its effect in the alteration of the metabolism, consequently affecting the cancer cell survival. Our data demonstrated that PTC-derived cells, particularly B-CPAP cells, harboring BRAF, TP53 and hTERT mutation, displayed the most perturbed metabolism and altered redox homeostasis, as reported by changes in metabolites and carriers involved in energetic pathways, and by changes in antioxidants, ROS and electron carriers levels. According to the fundamental role of metabolic alterations in CSCs, our findings reported variations in metabolic pathways, particularly in glycolytic and TCA cycle metabolites in thyrospheres, containing CSCs, compared to non-cancer stem-like cell and in thyrospheres versus parental cells. Finally, our data highlighted the sensitivity of PTC-derived cells to the vitamin C and its anti-tumoral mechanism by modulating metabolism and redox balance reciprocally.